1. Field of the Invention
The present invention relates to safety devices for fifth wheel vehicles such as tractor trucks that pull trailers. More particularly the device and embodiments thereof shown herein relate to a device to combat the ever present danger of jackknifing suffered by tractor and trailer combinations on the highway.
2. Prior Art
Traffic related accidents involving tractors engaged in the towing of trailers cost the trucking industry over $60 billion dollars annually. A significant factor leading to accidents which contribute to such a huge cost is caused by the inherent weakness of the conventional attachment of trailer-pulling vehicles to their rear-mounted trailers.
Because of the long length of the trailers involved and the need to continually negotiate highways, streets and loading docks, a pivoted mount of the trailer to the tractor is a necessity. However, the flexibility provided by a pivoted attachment to the trailer has a down side, especially when the wheels on the front vehicle or trailer lose traction. When the tires lose their grip, the relative alignment between the center axis of the front vehicle and that of the towed trailer can rapidly exceed a critical angle, thereby causing a jackknife condition.
From the dawn of development of motorized vehicles engaged in pulling trailers at significant speeds, many anti-jackknife devices have been described and taught. These devices can be classified into two broad categories. In the first category, a braking apparatus is adapted to engage with the mounting engagement of the tractor to the trailer, more commonly known as a fifth wheel. Most such braking style devices employ a conventional disc or drum brake mechanism that controls the angle and speed at which the trailer will rotate in its engagement to the tractor by slowing the rotation of the fifth wheel engaged to the trailer. This type of design can also be employed to provide a dampening force that controls the rate of rotation.
The second broad category of anti-jackknife devices includes devices designed to mechanically limit the maximum articulation of the trailer in relation to the tractor. This is generally accomplished by cutting slots, installing cables, or mounting hard stops to limit the trailer from articulating past a certain maximum angle. Because there are many times such as backing up or turning sharp corners where such an angle-limiting device would cause a problem, an activation mechanism that interfaces with the limiting devices must be included to disengage them and thereby allow the trailer to rotate more than about 20 degrees during slow speed maneuvers.
One widely used example of the slot style of articulation limitation employs hydraulic or pneumatic actuating pins, usually mounted on the fifth wheel, which are inserted into an arcuate slot cut into the bottom of the trailer. One major disadvantage of this design is that it is impossible to install a sufficiently large pin and corresponding actuating cylinder without redesigning the conventional kingpin latching mechanism on the more popular fifth wheels. Because it would be prohibitively expensive to replace all of the fifth wheels in a medium to large fleet in addition to purchasing the anti-jackknife device, this type of articulation limiting component is used sparingly. Another concern limiting the deployment of this type of system is the resulting reduction in strength caused by cutting large mounting holes in the fifth wheel and long slots in the bottom plate of the trailer.
Another scheme employed to limit rotational movement uses cables attached to the tractor and trailer. While this can be an effective method of preventing jackknifing, such devices require the driver to attach and detach heavy, dirty cables every time a new trailer is hooked up to the tractor. This is not only a nuisance but is also not a passively employed restraint, and disliking the task, drivers will often neglect to perform it at all, or if inexperienced, they may improperly attach the cables, potentially creating an unsafe condition. Like the pin mechanisms above, these cable devices can be very expensive, especially as a retrofit, since the length of the cables must change to accommodate sharp turns at low speeds which requires a cable winding mechanism. The bulk of such an apparatus to maintain the cables in the desired length must be mounted on the trailer which is not desirable since this greatly increases the cost to the trucking companies. This is because as a general rule most trucking companies have at least twice as many trailers as tractors.
Several patents teach the use of the fifth wheel component itself as a hard stop to restrict the rotational movement of the trailer such as in U.S. Pat. No. 5,135,248 (Keiserman) or U.S. Pat. No. 4,068,860 (Meyers). However, engagement of these types of devices require an extensive support structure mounted on the trailer to support the resulting side stress, increasing the cost.
Another probably more practical anti-jackknife device involves mounting lugs or stop blocks to the bottom of each trailer to be engaged with a tractor. Prior art describes such a scheme wherein the fifth wheel itself, or protruding lugs attached to the fifth wheel, are employed to interfere with the stop blocks mounted on the trailer. These types of devices are mainly used to protect the cab of the tractor from damage at very slow speeds and when turning sharply as would occur when picking up or dropping off the trailer.
U.S. Pat. No. 3,963,265 (Kornoelje) and U.S. Pat. No. 4,991,863 (Hosmer) teach an active mechanism mounted directly on the front of the fifth wheel to engage with blocks mounted on the bottom of the trailer. The actuating mechanism allows for full trailer rotation at lower speeds and jackknife protection above a certain speed threshold. However, Komeolje's design may not easily withstand the forces of the larger tractor-trailers during a jackknife situation and it is incompatible with most of the fifth wheels currently in use. Hosmer depicts a device with substantially more strength than Komeolje, but this strength comes at a cost since it requires substantial modifications to the fifth wheel, or more likely requires a custom fifth wheel altogether. Hosmer's patent also relies on the strength of the actuating cylinder to limit the angle of rotation which requires a cylinder of considerable size and cost.
U.S. Pat. No 3,730,555 (Keller) shows a pivoting “bumper” assembly mounted on the end of the tractor behind the last set of tires. The pivoting mechanism allows the bumper to engage the stop blocks on the trailer when jackknife protection is required. Whereas Keller's patent shows substantial strength, it does not compensate for movement when the tractor is tilted up or down relative to the trailer as would be seen, for instance, at the crest of a hill which could have devastating consequences. Additionally, there is a substantial cost associated with installing the extensive reinforcing members of Keller which is likely to have prevented any significant deployment by cost conscious truckers.
As such, there is an unmet need for an anti-jackknife device for tractor trailer combination vehicles. Such a device should minimize the number of components required to be mounted to the trailer to thereby minimize overall cost. Such an anti-jackknife device can be manual in engagement or would in a preferred form be passive in its engagement and activation such that it is automatically activated above a certain threshold speed and deactivated to allow turning and backing up of the trailer at slower speeds. Such a device should eliminate or minimize the labor of the driver or other workers to employ it, thereby encouraging its use with experienced drivers and not requiring any special instruction for newer drivers. Still further, such an anti-jackknife device should be constructed to transfer the forces developed in anti-jackknife situations to the tractor frame and should be able to work no matter what the angle of the front of the trailer to the rear of the tractor. Additionally, such a device should be easily attached to the vast majority of conventional tractors without the need for any substantial modification to the tractor or fifth wheel mounted upon it.